refunds on faulty goods

I bought a remote control car on 13/ 12 15. I charged the battery as per instruction and when my son played with it, after 5 minutes it did not work properly. The following day I took it back and explained the situation. Thinking it was a faulty battery the manager replaced the battery and tested the car in the shop. It did exactly the same after a few minutes. We opted to take a smoothie maker in its place. Now that we want to claim our money back on the item (7day money back guarantee?), we are told that it cannot be done as the are no cash refunds on toys. The toy in question was faulty out of the box. Had it worked properly we would not have brought it back in the first place. Does this mean that when you buy toys from Homemark that you are taking a gamble with your money because if it do not work then you have to buy something else from them although you do not want any of their offerings.